refactor(api): modularize assistant router workflow

packages/api/src/router/assistant-tool-results.ts

@@ -0,0 +1,46 @@
+type AssistantToolResult = {
+  content: string;
+  data?: unknown;
+};
+
+export function readToolError(result: AssistantToolResult): string | null {
+  if (result.data && typeof result.data === "object" && result.data !== null && "error" in (result.data as Record<string, unknown>)) {
+    const error = (result.data as Record<string, unknown>).error;
+    return typeof error === "string" ? error : null;
+  }
+
+  try {
+    const parsed = JSON.parse(result.content) as unknown;
+    if (parsed && typeof parsed === "object" && "error" in (parsed as Record<string, unknown>)) {
+      const error = (parsed as Record<string, unknown>).error;
+      return typeof error === "string" ? error : null;
+    }
+  } catch {
+    // tool content may be plain text
+  }
+
+  return null;
+}
+
+export function readToolSuccessMessage(result: AssistantToolResult): string | null {
+  if (result.data && typeof result.data === "object" && result.data !== null) {
+    const data = result.data as Record<string, unknown>;
+    if (typeof data.message === "string" && data.message.trim().length > 0) return data.message;
+    if (typeof data.description === "string" && data.description.trim().length > 0) return data.description;
+  }
+
+  try {
+    const parsed = JSON.parse(result.content) as unknown;
+    if (parsed && typeof parsed === "object") {
+      const content = parsed as Record<string, unknown>;
+      if (typeof content.message === "string" && content.message.trim().length > 0) return content.message;
+      if (typeof content.description === "string" && content.description.trim().length > 0) return content.description;
+    }
+  } catch {
+    // tool content may be plain text
+  }
+
+  return typeof result.content === "string" && result.content.trim().length > 0
+    ? result.content
+    : null;
+}